Structural requirements for full titanium containers

Structural requirements for full titanium containers
  Full titanium container
  A full titanium container means that the main components, such as housings, heads and takeovers, are made of titanium, and secondary components may be made of non-titanium, for example, flanges and their connecting bolts can also be made of carbon steel.
  The minimum thickness of the all-titanium container housing is 2mm, which mainly considers meeting the thickness requirements of the welding process and ensuring the geometric tolerance of the welding process, meeting the stiffness requirements required during the manufacturing, transportation and lifting process, and saving titanium and reducing costs.
  Design selection principles
  Since the mechanical strength of titanium is significantly reduced at temperatures greater than or equal to 200 degrees C, and the elastic modulus of titanium is low, it is not appropriate for full titanium structures to be used at high temperatures, high or medium pressures and on large equipment.
  The allowable temperature of the all-titanium pressure vessel should not exceed 250 degrees C, and it is considered that the pressure is 0.5MPa, and the whole titanium structure is more economical for small and medium-sized containers with a temperature below 150 degrees C. When calculating thicknesses greater than 13mm in terms of investment costs, it may not be economical to use pure titanium.
  Structural requirements
  Although the all-titanium container is somewhat similar in structural design to stainless steel, due to some special properties of titanium itself, it is unique in design and manufacturing, so in structural design, it is important to pay attention to the following points:
  1) In the design of the welding structure, the welding site must be made easy to operate the hydrogen arc welding tool, and all welding joint areas at high temperature (above 400 degrees C) can be effectively protected.
  Titanium can be used in combination with almost any element in a molten state, so special protection must be taken during welding and thermal processing.
In order to achieve effective protection purposes, the structure of components should be simple, the shell on the take-over opening as much as possible perpendicular to the axis of the housing, in order to protect the fixture production is convenient, the protection effect is better.
  2) Strictly avoid steel, titanium mutual melting welding structure. Because other metals such as iron are fused into titanium welds, hard and brittle intermediate metal compounds are formed, greatly reducing weld plasticity, except for explosive welding and brazing, titanium and steel cannot be welded.
  3) The blunt edge clearance of the butt welding joint should be appropriate.
The blunt edge gap of the butt welding joint of the all titanium pressure vessel is smaller than that of steel, due to the high melting point of titanium, poor thermal conductivity, small thermal capacity and large resistance coefficient, and the large fluidity of the metal in the welding melting pool.
  4) The design of titanium containers should ensure the continuity of the structure and the smooth transition of the welding joints, and try to avoid stress concentration.
  5) The bending and turning edge of titanium components should adopt a larger bending radius (compared with steel), and a smaller expansion pipe rate should be used when expanding the tube.
  6) Industrial pure titanium in some media easy to produce crevice corrosion, in the design, treatment of containers in contact with these media, should try to avoid the appearance of crevices and stagnant areas, in the crevices using gap-resistant titanium alloy (such as titanium palladium alloy) or coating.
  7) In designing and handling containers in contact with conductive corrosion media, if titanium and other metals are found to be in contact with other metals that can lead to galvanic corrosion, structural measures (e.g. the use of a third material as a transitional layer) or anode protection shall be taken.
  8) In the design of corrosion-prone equipment, the flow rate of the corrosion medium should be lower than the critical flow rate, and try to avoid sudden changes in the flow rate or flow rate, or in areas prone to corrosion and erosion to set up protective bezels.
  (1) When the medium is corrosive or abrasive and ρv2>740kg/(m.s2) or the medium is non-corrosive or abrasive, but the ρv2>2355kg/(m.s2) (ρ is media density, kg/m3, v is the line speed of the material flow, m/s), the material inlet should be set up anti-flushing plate.
  (2) When the corrosion medium is cut into the equipment, or the inlet pipe is facing the wall of the tube, and the distance between them is less than 2 times the outer diameter of the tube, the protective plate should be set.

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